Three years ago, James Sims couldn’t sleep. He stayed up late, maybe catching four or five hours of shut-eye, maybe dining on a few hundred calories of junk food in the wee hours of the morning.

He was a major-college running back, and a decent one at that, but he was also a college student. He did little that would be considered conducive to being an All-Big 12 running back. So if it was impressive that he rushed for 742 yards as a freshman in 2010, it might have been even more amazing that Sims did it all while not being in particularly good shape.

Last week, Sims sat at a table on the track inside Memorial Stadium, scribbling his autograph on poster after poster. It was Fan Appreciation Day at Kansas, and Sims was a wanted man. One year after rushing for 1,013 yards in nine games as a junior, Sims is entering his senior campaign with designs on being the most complete running back in the Big 12.

And when asked his secret — how he went from being a slightly flabby freshman to 1,000-yard rusher, Sims offered an answer that probably sounds good to anyone that’s ever attempted to work on an empty tank.

“Rest,” Sims said. “Gotta sleep.”

It’s eight or nine hours now, Sims says, and maybe it’s maturity. When he arrived on campus four years ago, he was a Mark Mangino recruit who had committed to Kansas — then kept his promise when Mangino was sacked for Turner Gill. Growing up in Irving, Texas, Sims had known then-KU assistant David Beaty for years, and Beaty always told Sims that he’d coach him in college someday.

“He was a like a father figure to me,” Sims said.

Beaty, who left for Rice in 2010, never got the chance, but Sims headed for Lawrence anyway. He rushed for more than 700 yards in his freshman and sophomore seasons, but the program went into a sharp decline, winning five games over his first two years.

Sims was a perfectly adequate running back in a perfectly bad program. But his junior year served as a turning point. First came the hiring of Charlie Weis in December 2011, and then came an arrest for driving under the influence in April. Sims had never been in trouble before, and the disappointment from the mistake served as motivation for the rest of the summer.

Eat healthier. Go to bed earlier. Keep life and football in a productive order.

“If you look at a picture of him from his freshman year to now, he’s totally different,” KU running backs coach Reggie Mitchell said. “And even the end of last season to now, he looks better.”

In a program that still has more question marks than answers, Sims is as close to a sure thing as there is. After rushing for 1,000 yards last year, Weis and Mitchell say Sims is perhaps playing better than ever before.

It’s one reason why Weis felt comfortable moving junior Tony Pierson into a hybrid receiver/running back role. And despite the return of former four-star running back Darrian Miller and the presence of senior Taylor Cox, Sims has continued to evolve into the Jayhawks’ leading back during fall camp.

“The best thing I like about James Sims is, with all of these running backs, he is still clearly No. 1,” Weis said. “He’s tough, he has good vision (and) it’s important to him.”

Last year, Sims often exited the huddle and saw the opposing defense stacking the line. It was a weekly reminder that Kansas couldn’t move the ball through the air — and the opponents knew Sims was about to get the ball.

“We were coming in week in and week out, knowing the defenses were going to try to stop the run,” Sims said. “And we just still ran the ball.”

This year, the hope is that KU’s passing game will improve, and Sims will have more lanes to run. In KU’s open scrimmage, Sims broke free for a 63-yard touchdown in the early minutes. It was an impressive display of speed and stamina — the kind of run that Sims would have struggled to complete as a freshman. As a senior, he appears plenty rested.

“It’s just kept me humble,” Sims said. “It’s just another step to just get better. Obviously, there’s other talent out there. And you’ve just got to work on the little things. The little things will separate you being in the pack.”